Intracerebral inoculation (ic) of mice with Theiler's murine encephalomyelitis virus (TMEV) provides an experimental animal model system that is useful in understanding how a persistent CNS virus infection leads to chronic demyelination, as might be the case in multiple sclerosis (MS). The overall goal of the proposed research is to elucidate the molecular basis of virus-host and virus-cell interactions in TMEV induced demyelinating disease. TMEV persistence is required to "drive" the demyelinating process, but exactly how demyelination occurs is still disputed. We believe that there is a central role for virusspecific DTH mediated by MHC class-II restricted CD4+ Th1 T cells in demyelination. Monocytes that are recruited into the central nervous system (CNS) differentiate into macrophages that: (a) allow viral persistence and (b) lead to bystander damage of myelin membranes. However, once TMEV establishes a persistent infection, the virus spreads to and productively infects oligodendrocytes, and possibly other cells. Recently, we have shown that TMEV replication is restricted in macrophages but productive in oligodendrocytes. As a result of binding to and/or infection of macrophages, TMEV induces programmed cell death (apoptosis), the hallmarks of which are prominently observed in the CNS white matter. Thus, the virus-macrophage interaction is an important element in TMEV persistence. Since TMEV persistence is required for demyelination, we wanted to know the responsible viral genetic elements as this might provide insight into the mechanism(s) of persistence. Use of recombinant TMEV mapped a viral persistence determinant to sequences encoding the capsid, and fine scale mapping suggested that this determinant is conformational in nature. Thus, the virus-cell receptor interaction is also an important element in TMEV persistence. In this Project, we plan to identify the attachment factor GDVII virus uses to bind to cells and further characterize the role of heparan sulfate proteoglycans in GDVII virus infection (aim 1), use immunological, molecular and biochemical approaches to identify the TMEV cellular receptor that has resisted identification over the years (aim 2), and further characterize TMEV-induced programmed cell death ( in murine macrophages (aim 3).